During fabrication of integrated circuits, it is often desirable to planarize and/or polish the surface of a semiconductor wafer. One method of performing these tasks is referred to as chemical mechanical planarization (CMP). In general, the CNT process involves rotation or random movement of a wafer on a polishing pad in the presence of a polishing slurry. The polishing pad is typically formed of a polyurethane material.
Downward pressure on the wafer against the pad, rotational speed of the wafer and the pad, slurry content and pad characteristics determine the rate at which material is removed from the surface of the wafer, and the uniformity of the resulting wafer surface.
Determination of how long a wafer should be planarized or polished has proven to be a difficult task An apparatus and method for in-situ measurement of the thickness of a material to be planarized for CMP end point determination is described in U.S. Pat. No. Re. 34,425 to Schultz.
Methods of controlling the pressure exerted on the wafer against the pad, rotational speed or random- movement of the wafer on the pad and slurry composition are well known in the art. Condition and performance characteristics of the polyurethane pad are more difficult to determine. The ability of a pad to planarize the surface of a wafer varies substantially from pad to pad and over the life of an individual pad.
After a wafer has been through the CMP process the pad will be conditioned to prepare it for another wafer. The conditioning process comprises a controlled abrasion of the polishing pad surface for the purpose of retuning the pad to a state where it can sustain polishing. The ability of the conditioning process to return the pad to a state where it can efficiently planarize an additional wafer is dependent upon the pad itself and the conditioning parameters. After planarizing several hundred wafers, the pad may no longer be useful for planarizing wafers despite the conditioning process.
The ability to predict performance characteristics of new and used polyurethane pads would be a great benefit to users and manufacturers of such pads.